basement rock -- n. The oldest rocks in a given area; a complex of metamorphic and igneous rocks that underlies the sedimentary deposits. Usually Precambrian or Paleozoic in age.

basin -- n. Any large depression in which sediments are deposited.

Basin and Range Province -- n. One of the most extensive systems of fault-bounded mountains separated by sediment-filled valleys, extending across Idaho, Oregon, Nevada, Utah, Arizona, New Mexico, California, and northern Mexico. Basin and Range topography The surface features typical of the Basin and Range Province.

bedrock -- n. The general term referring to the rock underlying other unconsolidated material, i.e. soil.

biostratigraphy -- n. The study of rock layers (e.g., distribution, environment of deposition, age) based on their fossils; biostratigraphic- adj.

biostratinomy -- The study of what happens between the death of an organism and burial. Part of taphonomy.

blueschist -- Metamorphic rock formed under great pressures, but not so great temperatures.

brackish -- adj. Slightly salty.

braided river -- n. A river characterized by a network of channels that split and entwine, rather than a single channel for water and sediment. Braided rivers are common in upland areas closer to mountain fronts where the slope, and consequently water velocity, lessens and the river begins to deposit sediment. Braiding is the result of the channel becoming clogged with sediment.

breccia -- n. A rock composed of angular fragments of older rocks; distinguished from a conglomerate in that the component rocks are not rounded and worn.

calcareous -- adj. Term used to describe a structure, secreted by an organism, that consists of or contains calcium carbonate (CaCO3), e.g., the shell of a bivalve.

caldera -- n. A large circular volcanic depression, often originating due to collapse.

caliche -- n. A sedimentary deposit commonly made of calcium carbonate and formed from the leaching of minerals from the top layers of soil. Caliche deposits characterize arid and semi-arid environments.

carbonate -- n. A mineral composed mainly of calcium (Ca) and carbonate (CO3) ions, may also include magnesium (Mg), iron (Fe) and others. n. Rock or sediments derived from debris of organic materials composed mainly of calcium and carbonate (e.g., shells, corals, etc.) or from the inorganic precipitation of calcium (and other ions) and carbonate from solution (seawater).
For example, limestone or dolomite.
carbonate platform - n. A broad (hundreds of meters), flat, shallow submarine expanse of carbonate rock, more common in the early-middle Paleozoic.
carbonate bank – n. A narrow (tens of meters), fairly flat, shallow, submarine plateau of carbonate rock, more common from the middle-late Paleozoic to the present, e.g., the Bahama Banks.

casts -- Fossils formed when water containing minerals leaks into a mold.
The minerals harden to form a copy of the original structure or organism.

cenote -- n. Mayan word for a sinkhole formed when fresh water dissolves limestone below the surface and the overlying rocks collapse.

clast -- n. An individual grain or constituent of a rock; clastic- adj. Describes a rock or sediment composed mainly of fragments of preexisting rocks or minerals that have been transported some distance from their place of origin, e.g., sandstone, shale.

compactions -- Fossils that have undergone some degree of flattening of their three-dimensional structure.

compression -- Fossil formed when an organism is flattened
(compressed) and a thin film of organic material from its body is left in the rock.

concretion -- n. A hard, rounded mass, commonly of silica, calcite, dolomite, iron oxide, pyrite, or gypsum, that formed within a rock from the precipitation of these minerals around a nucleus, such as a leaf, bone, shell, or fossil, and ranging in diameter from centimeters to meters.

continental crust -- The Earth's crust that includes both the continents and the continental shelves.

continental margin -- n. The ocean floor from the shore of continents to the abyssal plain.

continental rise -- n. Part of the continental margin; the ocean floor from the continental slope to the abyssal plain. The continental rise generally has a gentle slope and smooth topography.

continental shelf -- n. The part of the continental margin from the coastal shore to the continental slope; usually extending to a depth of about 200 meters and with a very slight slope, roughly 0.1 degrees; includes conetinental and oceanic sediments down to the ocean floor.

continental slope -- n. Part of the continental margin; the ocean floor from the continental shelf to the continental rise or oceanic trench. Usually to a depth of about 200 meters. The continental slope typically has a relatively steep grade, from three to six degrees.

core -- That portion of the interior of the Earth that lies beneath the mantle, and goes all of the way to the center. The Earth's core is very dense, rich in iron and the source of the magnetic field.

craton -- n. A part of the Earth's crust that has attained stability and has been little deformed for a long period of time, refers only to continents; cratonic- adj.

cross-bedding -- n. The arrangement of sedimentary beds tilted at different angles to each other, indicating that the beds were deposited by wind or flowing water.

crust -- n. The outermost layer of the Earth, varying in thickness from about 10 kilometers (6 miles) below the oceans, to 65 kilometers (about 40 miles) below the continents; represents less than 1 percent of the Earth's volume.

delta -- n. A low, nearly flat accumulation of sediment deposited at the mouth of a river or stream, commonly triangular or fan-shaped; deltaic– adj.

dendrites -- n. Small branching patterns on rocks made of iron and manganese oxides that show the passage of fluids through the rock.

deposition -- Any accumulation of material, by mechanical settling from water or air, chemical precipitation, evaporation from solution, etc.

diagenesis -- n. Any sort of chemical, physical, or biogenic change that occurs in fossils and sediments after their deposition. Physical erosion of a shell in a river, dissolution of carbonate in acidic conditions, and microbial invasion of a bone are all forms of diagenesis. adj. diagenetic

diatomite -- Diatomite, or diatomaceous earth, is a siliceous sedimaentary rock formed from the accumulations of diatoms or other nanoplankton.

esker -- n. A ridge of glacial sediment deposited by a stream flowing in and under a melting glacier.

estuary -- n. An area where fresh water comes into contact with seawater, usually in a partly enclosed coastal body of water; a mix of fresh and salt water where the current of a stream meets the tides; estuarine– adj.

evaporite -- n. a deposit of salt minerals (e.g., halite, gypsum, anhydrite) left behind by the evaporation of seawater, usually forms within a restricted basin.

fault -- n. (v.) A fracture, or large crack, in the Earth's crust where one side moves up/down/sideways relative to the other; fault block- n. pieces of crust that have slipped into or alongside a fault; fault zone- n. an area with multiple faults.

felsic -- Term used to describe the amount of light-colored feldspar and silica minerals in an igneous rock. Complement of mafic.

floodplain -- n. The flat area on either side of an active river channel that can be covered in water when the river is in flood. When the channel is breached, sediment-laden waters spread across the floodplain. When the waters recede, a layer of sediment is left behind. When the floodplain is not covered with water, it commonly supports vegetation and soil formation.

focus -- The initial point within the Earth that ruptures in an earthquake, directly below the epicenter.

gastroliths -- n. Fossilized gizzard stones, usually only applicable in the study of fossil reptiles.

geologic maps -- Maps that show the types and ages of rock of an area.
These maps are used by paleontologists to find areas that are likely to contain fossils they are interested in.

glass -- A non-crystaline rock that results from very rapid cooling of magma.

granite -- Highly felsicigneousplutonic rock, typically light in color; rough plutonic equivalent of rhyolite. Granite is actually quite rare in the U.S.; often the term is applied to any quartz-bearing plutonic rock.

hotspot -- n. A localized, somewhat persistent (tens of millions of years), and relatively fixed zone of mantle melting, inferred from surface volcanic activity. Evidence of a hotspot's existence is left behind as tectonic plates move across it, for example, the Hawaiian Islands.

hydrothermal vent -- n. A place on the seafloor, generally associated with spreading centers, where warm to super-hot, mineral-rich water is released; may support a diverse community of organisms.

hypersaline -- adj. Extremely salty, having much more salt than normal seawater.

island arc -- n. A curved chain of islands that rise from the sea floor, usually near a continent. The convex side usually faces the open ocean, while the concave side usually faces the continent, e.g., the Aleutian Islands in Alaska; volcanic arc- syn.

isotope -- One of two or more variations of the same chemical element, differing in the number of neutrons not the number of protons.

kame -- n. A short, steep-sided knoll of glacial sediment.

karst -- n. A type of topography formed by dissolution of rocks like limestone and gypsum that is characterized by sinkholes, caves, and subterranean passages.

kettle lakes -- n. Lakes formed as water fills a hole formerly occupied by a block of stranded ice.

lava -- Any molten material that is extrusive or volcanic, or the rock that forms from a molten extrusive.

loess -- n. A widespread, loose deposit consisting mainly of silt; most loess deposits formed during the Pleistocene as an accumulation of wind-blown dust carried from deserts, alluvial plains, or glacial deposits.

lowland -- n. (adj.) Large area of relatively low relief, usually applied to coastal regions that do not rise high above sea level. upland, highland – ant.

mafic -- Term used to describe the amount of dark-colored iron and magnesium minerals in an igneous rock. Complement of felsic.

mantle -- That portion of the interior of the Earth that lies between the crust and the core.

marine terrace -- n. A platform of marine deposits (typically sand, silt, gravel) sloping gently seaward. Such a platform may be exposed along the coast, forming cliffs, due to uplift and/or the lowering of sea level, e.g., marine terraces of coastal Southern California.

marl -- n. A loose, crumbly deposit consisting of clay and calcium carbonate and formed in marine or freshwater conditions.

melange -- A body of rocks consisting of large blocks (mappable size) of different rocks jumbled together with little continuity of contacts.

metamorphic rock -- Any rock derived from other rocks by chemical, mineralogical and structural changes resulting from pressure, temperature or shearing stress.

metamorphism -- n. The process of altering the chemical or mineralogical composition of a rock through different amounts of heat and pressure below the surface of the Earth; metamorphose- v; metamorphic - adj.

microfossil -- n. A very small fossil, best studied with the aid of a microscope, e.g. foraminifera, radiolarians, and small vertebrate fossils such as teeth. macrofossil– ant.

mineralization -- The process of replacing any organism’s original material with a mineral.

molds -- Fossils formed when the sediment surrounding a buried organism hardens. When the organism decays, its impression is left in the rock and can be seen if the rock is broken open.

moraine -- n. A mound or ridge of sediment deposited by a glacier; lateral moraine- n. deposited to the side of a glacier; terminal moraine- n. deposited to the front of a glacier; ground moraine- n. deposited on the land surface.

oceanic crust -- n. The Earth's crust which is formed at mid-oceanic ridges, typically 5 to 10 kilometers thick with a density of 3.0 grams per centimeter cubed.

plate -- n. Rigid parts of the Earth's crust and part of the Earth's upper mantle that move and adjoin each other along zones of seismic activity. The theory that the crust and part of the mantle are divided into plates that interact with each other causing seismic and tecotnic activity is called plate tectonics.

plutonic -- Applies to igneous rocks formed beneath the surface of the Earth; typically with large crystals due to the slowness of cooling. Synonym of intrusive. Antonym of volcanic.

radio-carbon dating -- Method for determining the age of an organic substance by measuring the amount of the carbon isotope, carbon-14, remaining in the substance; useful for determining ages in the range of 500 to 70,000 years.

rebound -- v. To spring back after a weight has been removed.

red bed -- n. Sedimentary layers composed primarily of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of iron oxides; often used in reference to the Permian or Triassic sediments of the western U.S.

reef -- n. A large ridge or mound-like structure within a body of water that is built by calcareous organisms such as corals, red algae, and bivalves;
barrier reef- n. A reef growing offshore from a land mass and separated by a lagoon or estuary, e.g, the Great Barrier Reef of Australia;
patch reef- n. A discontinuous reef growing in small areas, separated by bare areas of sand or debris, often part of a larger reef complex.

regression -- (n) A drop in sea level that causes an area of the land to be uncovered by seawater.

replacement -- Fossilization process in which the original material in an organism is broken down and replaced by different minerals.

rift -- n. A long, narrow crack in the entire thickness of the Earth's crust, which is bounded by normal faults on either side and forms as the crust is pulled apart; v. To split the Earth's crust; rift zone- n. The area on continents where a trough bounded by normal faults is forming; the site of crustal extension, similar to that which occurs at mid-oceanic ridges; rift basin or rift valley- n. The long, and fairly wide trough that has formed as a section of the Earth's crust has dropped down along faults, e.g., African Rift Valley in East Africa.

rock cycle -- The process through which one type of rock (igneous, sedimentary, or metamorphic) is converted into another.

strike -- The direction or trend of a bedding plane or fault, as it intersects the horizontal.

subduction -- n. A geologic process in which one edge of one crustal plate is forced below the edge of another; subduct– v.; subduction zone- n. A long narrow area in which subduction is taking place, e.g. the Peru-Chile trench, where the Pacific Plate is being subducted under the South American Plate.

subsidence -- n. The sudden sinking or gradual downward settling of the Earth’s surface with little or no horizontal motion.

syncline -- A fold of rock layers that is convex downwards. Antonym of anticline.

taphonomy -- n. The study of the death, decay, burial, and fossilization of an organism. Essentially, taphonomy describes everything that happens to an organism between the time it dies and the moment its remains are discovered. Understanding why organisms are or are not preserved over time helps explain the biases seen in the fossil record. Taphonomy is often broken into two parts, biostratinomy and diagenesis.

tectonic -- adj. Describing the forces that cause the movements and deformation of Earth’s crust on a large scale, also describes the resulting structures or features from these forces.

terrane -- n. A general term used to refer to a piece of the crust that is usually smaller than a continent but larger than an island; exotic terrane- n. terrane that has an unknown origin or a different origin than its surrounding rocks.

topography -- n. The relief features of the Earth's surface, above and below sea level; the set of landforms in a region.

trace fossil -- Evidence left by organisms, such as burrows, imprints, coprolites, or footprints. Trace fossils are not preserved parts of the organism.

transgression -- (n) A rise in sea level relative to the land.

tuff -- n. A general term for consolidated rocks made of material ejected from volcanic explosions.

turbidite -- n. The sediments or rocks that formed as a result of a turbidity flow.

turbidity current -- n. A bottom fast-flowing current that moves down a slope, depositing suspended sediments over the floor of a body of water

turbidity flow -- n. A flow of dense, muddy water moving down a slope due to a turbidity current

unconformity -- Any interruption of the continuity of a depositional sequence.

undifferentiated -- adj. Unable to distinguish between. Undifferentiated rocks: rocks for which it is not possible to specify finer age divisions.

upland -- n. (adj.) An area that is higher relative to the surrounding areas, but not mountainous; highland– syn.; lowland– ant.

uplift -- n. (v.) The process or result of raising a portion of the Earth’s crust through different tectonic mechanisms.

volcanic -- adj. Describes the action or process of magma and gases rising to the crust and being extruded onto the surface and into the atmosphere; also applies to the resulting igneous rocks that cool on the surface of the Earth, including beneath water, which typically have small crystals due to the rapidity of cooling. volcanically - adv. extrusive - syn. plutonic - ant.

volcanic arc -- n. A curved chain of islands that rise from the sea floor, usually near a continent. The convex side usually faces the open ocean, while the concave side usually faces the continent; island arc - syn.

volcanism -- n. The process by which magma and associated gases rise to the Earth’s crust and are extruded, or expelled, onto the surface and into the atmosphere.

weathering -- n. The physical, chemical, and biological processes by which rock is broken down into smaller pieces.